The present invention relates to the molding of fluent materials and is particularly concerned with improvements in apparatus for use in injection molding of precision made articles manufactured on a mass production basis.
While the invention has a number of applications it will be illustrated by reference to the production of improved oil seals, which are commonly made of curable elastomeric materials such as nitrile, acrylate and silicone rubbers, as well as more conventional synthetic and natural rubbers.
Compression and transfer molding have been very commonly used in the manufacture of such seals while injection molding has been used to a lesser extent in this industry. Injection molding of curable parts of this type has involved problems which have been difficult to overcome. In the manufacture of a typical oil seal it is necessary that the mold unit be precisely formed since seals are often required to be made to very close tolerances in order that they will fit on highly precise parts made to fine tolerances. When in use they are expected to last for extended periods. Consequently, when seals are mass produced, which is necessary for economy of production, it is a requirement that the seals be characterized by great uniformity of dimension and that the finished elastomeric material be very uniform throughout its entire extent so as to exhibit uniform properties of flexure and wear. This is difficult to achieve with injection molding apparatus annd procedures.
One form of injection molding apparatus and procedure which has solved a number of problems encountered in oil seal production is disclosed in U.S. Pat. No. 3,773,454 granted Nov. 20, 1973 to Leslie A. Horve, Jerry D. Reichenbach and Kenneth F. Gabrys, which shows an injection molding apparatus including top and bottom mole assemblies adapted to be brought together along an aligned path so as to provide a mold cavity between spaced confronting faces which cavity opens at the bottom into an annular recess in which a metal stamping is adapted to be positioned with a portion extending into the mold cavity to which fluent rubber is fed by means of a center pouring well and connecting passages through which the rubber material may flow. The top mold assembly includes a spring backed stripper plate mounted on headed pins which depend so as to form guideways and downward limit stops for plate movement in an annular recess outboard of a land forming bottom face portion of relatively small width which seats on a flange portion of the stamping when the mold is fully closed for the molding operation. A bottom face portion of the stripper plate resiliently engages the top edge of an upstanding outer flange of the stamping as the mold members approach closed position. While this apparatus will provide a highly satisfactory seal unit of the desired characteristics, experience with this and similar molding apparatus has indicated the desirability of improving the apparatus, particularly, with a view to obtaining still more efficient operation, a longer life for the apparatus and greater adaptability in handling different sizes of seal units, especially, in the handling of seal units having a metal stamping portion to which a rubber body or lip portion is to be bonded.
It is a general object of the invention to provide an injection molding apparatus which is especially adapted for the molding of precision oil seal units, which will operate with a high degree of efficiency, which will produce successive seal units which are of uniform dimensions and quality, which requires a minimum of maintenance and which is subject to mimimum wear.
A more specific object of the invention is to provide a molding apparatus of the type having top and bottom mold assemblies with cooperating surfaces defining a mold cavity and with improved means for holding in proper position a metal stamping so as to bond to a portion thereof a rubber body or lip portion which is formed in the mold cavity.
A further object of the invention is to provide a molding apparatus which is particularly adapted for injection molding of oil seals of the type having a metal stamping and a lip portion of rubber or similar moldable product wherein top and bottom mold assemblies are provided which cooperate in positioning the stamping and forming a mold cavity for the lip portion with improved hold down and stripper means which is highly efficient in operation and which is subject to mimimum wear so as to increase the life of the mold assemblies while enabling uniform mass production of the seal units.
To this end the invention embodies a molding apparatus particularly adapted for forming precision seal units, which apparatus includes top and bottom mold assemblies adapted to be opened and closed along an aligned path and having opposed surfaces which cooperate, in the closed position, to provide a mold cavity for forming from fluent rubber, or the like, a seal body, or lip member, in bonded relation to a portion of a metal stamping which is adapted to be seated in a recess adjoining the mold cavity, with the top mold assembly having a resiliently backed plate in the form of a ring member freely slidable in a recess therein, which ring member initially clamps the metal stamping in position and subsequently serves as a stripper when the mold assemblies are separated in order to remove the seal units, the ring member and associated recesses in which the metal stamping is received being capable of accommodating metal stampings of varyiing radial and axial dimensions within certain predetermined limits.
The manner in which the objects and advantages of the invention are achieved in practice will be apparent when reference is made to the accompanying detailed description of the preferred embodiment of the invention, which is set forth, by way of example, and illustrated in the accompanying drawings, wherein like reference numerals indicate corresponding parts throughout.